Keepers at ZSL London zoo began the mammoth task of counting the park's more than 700 species on Tuesday, using treats to entice some animals out for the annual stocktake.

From small invertebrates to larger mammals, creatures of all sizes are counted each year at the zoo in the center of the British capital. New additions for the 2017 census include four Humboldt penguin chicks and Sumatran tiger cubs Achilles and Karis.

Tallying up all the animals takes around a week and is a requirement of the zoo's license. Information collected is then shared with other zoos around the world to help in the protection of endangered species.

"It's an opportunity for all of the animal teams to go out and make a record of how many individual animals we've got on each section," Zoological Manager Mark Habben said, noting the zoo had some 712 species and more than 18,000 animals.

"At the end of June, Melati, our female Sumatran tiger, gave birth to a male and female and that for us is a real measure of success."